Microstructural Characteristics in Babbitt Coatings Deposited by LPCS

Studies have already established that the mechanical properties of Babbitt coatings significantly depend on the microstructural characteristics, such as the amount and distribution of intermetallic compounds dispersed in a soft solid solution matrix. For Sn–Sb–Cu-based Babbitt coatings, the formation of SbSn- and CuSn-based precipitates has a substantial influence on the resulting microhardness and thus determines the maximum load carrying capacity. Thermal spraying of Sn-based Babbitt coatings results in a relatively more refined structure of these precipitates than in common manufacturing processes, such as casting, due to the thermal processing conditions. This study aims to evaluate the effect of the temperature of the propellant gas and substrate temperature on the microstructural characteristics of Sn–Sb–Cu-based Babbitt coatings deposited by low pressure cold spraying (LPCS). The deposits were examined for their phase composition, microhardness and mesoscopic structure. It was found that the coatings were mainly composed of Sb2Sn23, Sb0.49Sn0.51 and Sorosite (CuSn or CuSb0.115Sn0.835), regardless of the substrate temperature or temperature of the propellant gas to be investigated. For a gas temperature above 300 °C, an increased microhardness was observed, which correlates with the appearance of a more homogenous distribution of Sb0.49Sn0.51 dispersed in a soft Sn-rich solid solution matrix.

The Microstructural Peculiarities of Beryllium Bronze after Heat Treatment

In this article, the microstructural peculiarities and properties of dispersion-hardened beryllium bronze with Ni and Ti are studied after quenching (780 °C) in a supersaturated solid solution and aging (320 °C, 3h). Decomposition of the α-solid solution matrix is implemented by means of an intermittent reaction with a primary allocation intermetallic χ-phase (type Be12Ti) with a VCT-lattice. It is shown that the strength properties (yield strength, micro-hardness) of the alloy more than double after aging.

Characteristics of Ni- Cr Binary Alloys Produced by Conventional Powder Metallurgy

The characteristics of Ni-Cr porous alloys containing 0.5 wt%Cr up to 12 wt%Cr were determined. The alloys were prepared from a mix of Ni-particles with filamentary shape and Cr-particles with irregular shape which then mixed with 0.5 wt% paraffin wax as a binder. The samples were formed by compaction and then sintered at 1200 °C for 1 h. The microstructure of samples was found to consist of a Ni-Cr solid solution matrix with X-ray energy dispersive analysis of Cr% less than 0.33 wt%. The matrix microstructure which composed of equiaxed grains (20-60 μm) surrounded high Cr content islands which also contained γ phase (Ni2.88 Cr1.22). The apparent density of the alloys was found to decrease with Cr content from 8.32 g/cm3 for samples containing 0.5 wt%Cr to 7.26 g/cm3 for samples containing 12 wt%Cr. Therefore, the estimated porosity was found to increase from 6.4% to 16.6% with increasing Cr content from 0.5 wt% to 12 wt%. The microhardness of the samples varied from 153.6 to 284.2 VHN for the equiaxed grains and from 119.6 to 240.6 VHN for the island areas.

A detailed microstructural and corrosion analysis of an additively manufactured magnesium alloy produced by selective laser melting

Magnesium (Mg) alloys have promising potentials for lightweight and biomedical applications. Although there has been a recent interest in producing Mg alloys (including AZ, ZK and WE series) using additive manufacturing (AM), the process-structure-corrosion properties relationships in AM Mg alloys are yet to be understood. Herein, the production of Mg alloy WE43 was achieved by selective laser melting (SLM). The alloy was investigated after SLM, hot isostatic pressing (HIP) as well as an additional solutionising heat treatment. Specimens were carefully characterised, whilst assessed and contrast relative to the conventionally cast alloy counterpart. Characterisation included detailed microstructural analysis employing analytical transmission electron microscopy, X-ray mapping, and electron backscatter diffraction, which revealed the SLM prepared specimens possess a unique microstructure comprising fine grains growing with a strong [0001] texture along the building direction. The SLM prepared specimens also revealed a low fraction of process-induced and metallurgical defects, reaching < 0.1% after optimising the SLM parameters and HIP treatment. The SLM prepared WE43 was found to be cathodically more active relative to the cast WE43 because of a fine distribution of zirconium-, yttrium- and oxygen-rich particles as well as the alterations in the chemical composition of the solid-solution matrix originating from the high cooling rates of SLM. It was revealed that the oxide particles were mainly sourced by powder and thus it is hypothesised that the corrosion of SLM prepared Mg alloys could be greatly improved once the influence of powder characteristics is further understood and controlled.

MULTICOMPONENT Al-BRONZE COATINGS THERMALLY SPRAYED ONTO TIN BRONZE SUBSTRATE: MICROSTRUCTURAL, MECHANICAL AND CORROSION CHARACTERIZATION IN A 3.5% NaCl SOLUTION

In this work, multicomponent Al-bronze alloys coated Tin-Bronze substrates, fabricated by thermal flame spraying, are characterized by X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. Mechanical characterizations are also presented: microhardness measurement and friction coefficient. The electrochemical behavior of tin-bronze samples uncoated and coated with multicomponent Al-Bronze coatings is studied in NaCl 3.5% solutions using potentiodynamic polarization curves and polarization resistance measurements. The microstructure of the coatings has a lamellar morphology. Each lamella is constituted of a mixture of Cu3Al globular micro precipitates ([Formula: see text]-phase) uniformly distributed over the solid solution matrix ([Formula: see text]-Cu). An oxide based on Cu, Al and Fe is also present in very low concentration. [Formula: see text]-phase is unexpected because it is present only above 570∘C in the Cu-Al phase diagram. Compared with the tin-bronze substrate, multicomponent Al-bronze coatings show a friction coefficient three times lower and have a better electrochemical behavior in 3.5% NaCl solution.

Coherent Precipitation and Strengthening in Compositionally Complex Alloys: A Review

High-performance conventional engineering materials (including Al alloys, Mg alloys, Cu alloys, stainless steels, Ni superalloys, etc.) and newly-developed high entropy alloys are all compositionally-complex alloys (CCAs). In these CCA systems, the second-phase particles are generally precipitated in their solid-solution matrix, in which the precipitates are diverse and can result in different strengthening effects. The present work aims at generalizing the precipitation behavior and precipitation strengthening in CCAs comprehensively. First of all, the morphology evolution of second-phase particles and precipitation strengthening mechanisms are introduced. Then, the precipitation behaviors in diverse CCA systems are illustrated, especially the coherent precipitation. The relationship between the particle morphology and strengthening effectiveness is discussed. It is addressed that the challenge in the future is to design the stable coherent microstructure in different solid-solution matrices, which will be the most effective approach for the enhancement of alloy strength.

Mechanical Properties of Ti-alloy Joint with Ti20Zr20Cu60-xNix (x = 10, 20, 30, 40 and 50) Filler Metal

The developed microstructure features a long with mechanical properties in vacuum brazing of commercially pure Ti-alloy using Ti20Zr20Cu60-x-Nix (x=10, 20, 30, 40 and 50) metallic filler. Brazing temperatures and holding times employed in this study were 1240-1279 K (967-1006oC) for a period of 10 min, respectively. The mechanical properties of brazed joints were evaluated by nanoindention at a constant peak load of 5000 μN and tensile tests. The number of intermetallic phase, such as NiTi2, Ti2Cu, (Ti, Zr)2Cu, (Ti, Zr)2Ni, β(Ti, Zr), α-Ti and NiTi. The solid solution matrix have been identified at 1279 K out of these different regions the NiTi2 rich region had the highest nanohardness of 17 GPa, It is interesting to note that among five different glasses, the Ti20Zr20Cu10Ni50 has the highest yield strength of 17 GPa, which is mainly due to NiTi2 phase. Based on the tensile test results all cracks propagate along the brittle intermetallic compounds like NiTi2 in the reaction layer the reduction of the strength of the joints and fracture behaviour upon propagation of the crack, which shows the morphological cleavage including facets characteristics.

Grain Refinement of AZ61 Alloy after ECAP Processing

Electron microscopy techniques were used to characterize the microstructure and deformation behavior of AZ61 alloy proceeded by ECAP. The commercial AZ61 alloy subjected to severe plastic deformation possesses a two-phase microstructure consisting of solid solution matrix and massive γ-phase Mg17Al12, or Mg17(Al,Zn)12 distributed mostly at grain boundaries. Based on selected area diffraction and electron back scattered diffraction applied to a sample after the third pass, it can be concluded that plastic deformation induced by ECAP occurs mainly by slip mode forming a high density network of dislocation inside the grains. The grains size was significantly refined to 1.4 μm after the third pass of ECAP. The refinement of grain size is probably due to polygonization process associated with formation of high angle grain boundaries due to dislocations rearrangement. (Al, Zn)12Mg17 precipitates of size scattered from 100 to 200 nm and also the primary precipitates of Al6Mn phase were observed in this alloy.

The Comparison of the Microstructure and Corrosion Resistance of Sand Cast Aluminum Alloys

The influence of different types of precipitation on the corrosion behavior was investigated in three aluminum-siliconmagnesium alloys. The microstructures of the alloys were studied through optical (OM) and scanning electron microscopy (SEM). The structures consisted of an α-Al solid solution matrix, Si eutectic crystals, secondary phases AlFeSi and AlMgFeSi (Chinese script), as well as Mg2Si. The corrosion behavior was examined with the use of a potentiodynamic polarization test followed by a SEM surface analysis. The results indicate that all the analyzed samples were in the passive state and AlSi10Mg was less reactive in the corrosive environment.